The present invention relates to a method for fitting a tubular roll mantle of a roll intended for a paper machine or equivalent with glide bearings, in which the roll mantle is supported on a stationary roll axle by means of hydraulic glide bearing elements acting upon the roll mantle or upon the roll ends. The bearing elements are hydraulically loaded by the effective pressure applied by a pressure medium. The roll is loaded from its exterior radially in the direction of at least one plane, i.e. in a so-called principal loading direction.
The invention also relates to a tubular roll that makes use of the method in accordance with the invention for a paper machine or equivalent. The roll mantle of the roll is revolvingly supported on a stationary roll axle by means of glide bearing elements that act upon the inner face of the roll mantle and/or upon the roll ends. The glide bearing elements are loaded by means of the pressure of a hydraulic pressure medium, while the roll is loaded from its exterior radially in the direction of at least one plane, i.e., in the so-called principal loading direction.
Tubular rolls in paper machines are ordinarily mounted or journalled on the roll axle at the ends of the roll mantle by means of roller bearings. Such a conventional mode of journalling has its advantages, for example, the fact that the journalling can be accomplished quite simply, and so far its costs have been considered to be relatively moderate. However, this conventional mode of journalling, in which the roll mantle is journalled on the axle permanently by its ends, is not suitable for all objects of use in paper machines. In quite a number of cases, the roll mantle must be able to move radially in relation to the roll axle, which characteristic is quite often required, e.g., for variable-crown rolls which are in nip contact with a back-up roll. By means of the crown variation means in a variable-crown roll, attempts are made to shape the roll mantle in the desired way especially in view of regulation of the profile of linear load. Therefore, the roll ends must also be able to move in the radial direction in relation to the axle in order that the profile of linear load could be controlled in the end areas of the roll. In addition to the profile-regulation properties in the end areas of the roll, the regulation of the loading in the end areas of the roll also affects the control of the temperatures in the end areas of the roll.
For this reason, such rolls have been developed in which the entire roll mantle can move in the direction of loading radially in relation to the roll axle. One roll of this type is described in the assignee's EP Patent No. 0 332 594. In the roll described in this reference, the end bearings of the variable-crown roll are not mounted directly on the central axle of the roll. Rather, the bearings are arranged on separate annular parts which can move radially in relation to the roll axle. The variable-crown roll in accordance with this reference is a nip roll, and the radial movement of the roll mantle is confined to the direction of the nip plane. The movement is accomplished so that hydraulic power units are arranged between the annular parts and the roll axle. The power units shift the end bearings by means of a hydraulic pressure medium toward the nip or away from the nip. The principal object of the device in EP '594 is to open and close the nip. There is also a large number of other rolls of similar type, which produce a substantially corresponding action accomplished by means of a somewhat different technique.
The fitting of a roll with roller bearings also produces considerable drawbacks and/or problems for the manufacture and operation of the roll. It is one particular drawback that the roller bearings require certain machining of the roll mantle. The wear of the bearings may also result in problems and, further, the roller bearings impose their restrictions in respect of the oil or fluid to be used in the roll. For example, the following properties can be considered as the weak points of the conventional mode of journalling.
Restrictions of speed: Even at present, the speeds of rotation of the rolls exceed the maximum permitted speeds specified by bearing manufacturers.
Precision of rolling: With the present technology, it is very difficult to increase the rolling precision of an assembled roll further. In a traditional roll, even if all the components (bearings, bearing spaces, outer face of mantle) are machined as precisely as possible, the defects are summed up in an assembled roll.
Fitting of a roll mantle with glide bearings is also known in the prior art. Such rolls with glide bearings are described, e.g., in U.S. Pat. Nos. 5,060,357 and 5,111,563. In the roll in accordance with the '357 patent, the roll mantle is provided with roller bearings arranged in the areas of its end pieces. The bearings are arranged on separate ring parts of a type similar to those described in EP '594. The roll is intended for use as a nip roll, and its roll mantle can move in the direction of the nip plane in relation to the axle, e.g., for the purpose of opening and closing the nip. Lateral support of the roll mantle, i.e. the support in the direction transverse to the nip plane, is provided by means of a complicated construction of glide bearings which endeavors to make the movement of the roll mantle take place exactly in the direction of the nip plane. It is a drawback of the construction that it is extremely complicated, for example, with a number of glide faces and arrangements of articulated joints, for which reason, the reliability in operation, controllability, and the dependability of the construction cannot be considered to be very good. It is a further problem of the apparatus in accordance with the '357 patent that forces transverse to the nip plane and applied to the roll from outside, i.e., the roll exterior, cannot be compensated for because such forces cause a disruption of the oil film between the glide shoes and the inner face of the roll mantle. In U.S. Pat. No. 5,111,563, an arrangement of lateral support of a roll with glide bearings is described, which arrangement is simpler than the apparatus of the '357 patent mentioned above. In this reference, the arrangement of the glide bearings in the lateral direction is accomplished by means of an arrangement of articulated joints that is likewise not capable of compensating for lateral forces applied to the roll from outside.